Explanation: Eris, a
dwarf planet
currently orbiting the Sun at about twice Pluto's distance,
has
been measured
to have about 27 percent more mass than Pluto.
The mass was calculated by timing the orbit of Eris' moon
Dysnomia.
Images taken with a ground-based
Keck telescope,
when combined with existing images taken by
Hubble Space Telescope,
show that Dysnomia has a nearly circular orbit lasting about 16 days.
Cataloged as 2003 UB313 only a year ago,
infrared images also showed previously that Eris is actually
larger in diameter than Pluto.
The plane of Eris' orbit is well out of the plane of the
Solar System's planets.
In the above drawing, a scientific artist has imagined Eris and Dysnomia orbiting our distant Sun.
No space missions are currently planned to Eris, although the robotic
New Horizons spacecraft bound for
Pluto has recently
passed Jupiter.